1. Field
The present invention relates to representation of geospatially-based data and, more specifically, enhancement of the representation of such data to improve the understanding of such data.
2. Discussion of Related Art
A geographic information system is an information system designed to associate data of various types with spatial or geographic coordinates. Typically, a geographic information system displays data overlaid on some type of map showing geographic or political boundaries. Hence, the geographic information system is slaved to an underlying map. Data are registered to geographic positions on various projections of the earth, such as Mercator, Hammer, Gnomic, or Eumorphic. However, in representing data on a standard map, misperceptions can arise, because visualizing data on a standard map inherently emphasizes regions with the greatest geographic area, while making the presentation of very small regions and the data associated with those small regions quite difficult.
One way in which to deal with the misperceptions caused by the sizes of the displayed geographic areas on a map is to “zoom in” on a specified portion of the map to see the displayed data in increased detail. “Zooming” or scaling displayed images is well known in the art. U.S. Pat. Nos. 4,686,580, 4,872,064, 5,384,904, and 5,485,563 disclose different techniques for scaling portions of an image or an entire image. The scaling techniques disclosed in these patents generally describe the uniform scaling of an image. Application of these techniques in a geographic information system application results in the scaling of selected regions of the displayed map in a uniform fashion. For example, if a map of the United States is displayed and the user elects to zoom in on the map area displaying California, Calif. and the areas surrounding it located within the zoom area, will be uniformly increased in size. The areas outside the zoom area will likely disappear from the display.
Geographic information systems providing for the display of geospatially-based data and providing for control of the size and resolution of the map underlying the data are also known in the art. U.S. Pat. No. 4,675,676, by Takanabe et al., discloses a vehicle map system that includes a control unit that manually or automatically enlarges or reduces the displayed map. Hence, as a vehicle comes closer to its desired destination, the displayed map is enlarged to show more of the details relating to the desired destination. U.S. Pat. No. 6,052,645, by Harada, also describes a vehicle map system in which a detailed map is displayed when a vehicle carrying the system approaches a specified location. Since the scaling used in the detailed maps is uniform, map information for areas outside the detailed map area is no longer displayed when the detailed map is displayed.
Implementations of geographic information systems may provide for several levels of scaling. Delorme describes, in U.S. Pat. No. 5,030,117, a digital global map generating system that provides a hierarchical map system that allows a user to progress from a first view of the world at a low resolution to segments of the world at increasingly higher resolutions. The map display is controlled such that the entire selected segment is displayed and the user can elect to either move up or down in the hierarchy by clicking on the display with a mouse or other pointing device.
As indicated above, registration of data to the underlying map is an important feature of geographic information systems. Miller et al., in U.S. Pat. No. 5,652,717, describe a technique for registering data from multiple sources with a geographic database and manipulating the data for display. Kruhoeffer et al., in U.S. Pat. No. 5,379,215, describe the registration of weather information with a terrain map to create a three-dimensional display. Berger et al., in U.S. Pat. No. 5,418,906, describe a method for converting data registered in one geographic information system database into another geographic information system by mapping the data in a specified geographic extent in the first GIS into the second GIS. A common feature of all these systems and methods is that the scale of the data displayed is uniform across the entire display. That is, a user will select a geographic area and the system will determine the appropriate display size and resolution to display the selected geographic area. Areas outside of the selected geographic area will not be shown to the user.
One type of map known in the art for relating underlying data to the size of displayed geographic or political boundaries is the area cartogram. The area cartogram scales areas within a map to conform to the data associated with the scaled area, while preserving, to some extent, the shape, orientation and contiguity of the scaled area. There are two types of cartograms: contiguous and noncontiguous. Both contiguous and noncontiguous cartograms are known in the art.
A contiguous cartogram is drawn so that the boundaries of the geographic or political units are tangent to one another. FIG. 1 shows an exemplary contiguous cartogram showing the population of the United States, with the size of each state representing the total population of that state. FIG. 1 also shows one of the major drawbacks with contiguous cartograms in that the shapes of the geographic or political units must be distorted to maintain common boundaries.
A non-contiguous cartogram is drawn so that the true geographic shapes of the geographic or political units are maintained after scaling the units. FIG. 2 shows an exemplary non-contiguous cartogram showing the population of the states of the southeastern United States. FIG. 2 also shows some of the major drawbacks of the non-contiguous cartogram: (1) the geographic or political units do not fit together to maintain the contiguous character of the original map and (2) the empty space between the units make it difficult to maintain the original shape of the area under study and to present it in a compact form.
A further limitation with both types of cartograms is that the scaling of the geographic or political units is normally based on a single data variable. The intent of a cartogram is to assist in the visualization of that data variable when it is coupled to geographic or political units. However, as noted above, the entire map area will be scaled based on that single variable. Hence, the representation of other data variables may be lost or underemphasized due to the cartogram scaling used for the first variable.
Geospatially-based data is often relevant only at a particular geographic scale, but at multiple locations. The data may, therefore, be widely distributed over a large geographic area and occur over long periods of time. Display of the data at a resolution that will allow the entire geographic area to be seen may result in the information display in informationally dense areas to be unreadable. Display of informationally dense areas using conventional geographical information systems may require users to perform multiple zoom functions to evaluate data at different locations at a high resolution or require that multiple displays be used. However, these methods may hide the geographic relationship between the areas in which the data is displayed. Analysts need advanced visualization techniques to correlate data associated as vastly different scales, distances, and times.
Hence, there is a need in the art for a method of generating maps with map entities sized according to data associated with the map entities, while maintaining shape and position relationships between the map entities. Further, there is a need in the art for providing this method in an automated fashion.